
It is a general change introduced in High Sierra and will affect any third-party (i.e. If you have installed the driver on an earlier version of macOS and then upgrade to 10.14, you should not need to enable the driver.
This behavior will only occur when installing a MOTU driver on Mojave for the first time. all still work fine with driver 2.5 and Logic still supports them in Mojave. Be sure to use the latest versions of both the Studio Manager V2 Host and Editor available on this Yamaha Pro Audio site. To display the Allow button, run the installer for the MOTU driver again. I have the most luck when the unitor is the only MIDI capable USB device. The USB-MIDI Driver is for use with Studio Manager V2 Host and Editor. The Allow button will disappear 30 minutes after installation. In the General section, click the Allow button. Customers need to install Yamaha USB-MIDI Drivers on their computer if they have an instrument with a USB TO HOST port (looks like a square USB port) on it, or when using our UX16 USB-MIDI Interface. After restarting, open System Preferences. Download and install the very latest installer for your MOTU interface. IMPORTANT NOTICE: When the Windows SmartScreen is displayed upon installing the driver, please perform the following. To enable the MOTU drivers, follow these steps: If your MOTU interface is not showing up in Audio MIDI Setup, MOTU Audio Setup, the MOTU Discovery App, or your DAW on High Sierra or Mojave, you might need to allow the driver in your System Preferences. In the Audio MIDI Setup app on your Mac, choose Window > Show MIDI Studio.
The system extensions for all newly-installed third-party software will automatically be blocked from running.
As of macOS High Sierra, Apple has introduced a new security measure.